It is well-known to treat polyamide substrates, such as catering, with compositions which impart resistance to staining by an acid dye, such as FD&C Red Dye No. 40. Such compositions are commonly referred to as stain-resists or stainresist agents.
For example, one class of known stain-resist agents comprises one or more sulfonated hydroaromatic-formaldehyde condensation products, for example, phenol-formaldehyde condensation products or formaldehyde-naphthol condensates. When stain-resist agents based on such condensation products are applied to polyamide substrates, they provide acid dye stain-resistance which resists removal by shampooing. But such treated substrates are prone to yellowing on exposure to ultraviolet light (UV) or to nitrogen oxides (NOx), or to combinations of UV and NOx exposure.
Another class of known stain-resists involves the use of hydrolyzed copolymers derived from maleic arthydride and ethylenically unsaturated compounds. Examples include hydrolyzed copolymers of realere anhydride and one or more of the following comohomers: ethylenically unsaturated aromatics, alphaolefins, alkyl vinyl ethers, and alkyl allyl ethers. Due to the ionic character of stainresist agents based on hydrolyzed maleic anhydride copolymers, polyamide fiber substrates treated with such stain-resists tend to be sensitive to high pH values, such as those that may often be encountered in commercial rug shampoos. As a result, in some cases, stain-resistance is partially or completely lost following shampooing. Such stain-resist agents show better resistance to yellowing on exposure to UV or NOx or a combination of UV and NOx, but poorer resistance to removal by shampooing than the sulfonated phenol-formaldehyde condensates.
Epoxy resins can be cured with carboxylic or polycarboxylic acids, and epoxy resins in combination with carbonlie acid-containing polymers can be applied to fiber substrates. For example, combinations of epoxy resins and copolymers of metbacklit acid have been applied to carpets and carpet yarns as anti-soilants for carpets and carpet yarns.
In view of the above-described considerations, it is apparent that there is a need to provide stain-resists for polyamide substrates which combine resistance to removal during commercial shampooing and resistance to yellowing caused by UV or NO.sub.x or both.